Induction coil



Dec. 12, 1939. D. PISAREV 2,182,820

INDUCTION COIL Filed Dec. 21, 1938 Patented Dec. 12, 1939 2,182,829

UNITED STATES PATENT OFFICE" '7 Claims. (Cl. 219-47) This inventionrelates to new and useful imred only after further heating. At anyinstant provements in induction coils, and more para portion of theobject mi y between its ends ticularly to a novel induction coil whichis pargives the appearance of a more intense redness ticularly adaptedfor use in high frequency heatthan the ends, an indication of highertemperamg apparatus for treating susceptors disposed ture. Theefliciency of a heating device of this I externally about the inductioncoil. type is considerably low since the entire length At the presenttime induction coils employed of the article to be heated does notreceive the in high frequency furnaces of this type are genfull force oraction of the flux or magnetic field erally of cylindrical or taperedshape, or otherinduced. The result of this is, of course, that wiseconform to the contour of the article around it requires operation ,ofthe furnace for a longer 10 it. It is desirable to employ a coil of thischarperiod of time than should be necessary to comacter in order thatthe coupling between the pensate for the time required to allow thesmallcoil and article being heated may be uniformly er amount of heat inthe ends to reach the demaximum throughout the length of the coil. siredtemperature. In any instance, consider- That is to say, since thecoupling between the able heat is dissipated or lost by radiation andcoil and the article being heated determines the conduction from theobject being heated. and heating action, and since the coupling at anythis longer period of time required for operation point along the axiallength of the coil depends of the furnace consequently results in aninupon the proximity of the coil at that point to crease in suchradiation and conduction losses.

the article, it is desirable to employ a coil For "skin hardening,excessive conduction into I) which conforms to the contour of the artheinterior of the article is undesirable.

ticle around it thus obtaining uniformly maxi- By the present invention,this deficiency of mum coupling and consequent maximum heatcoils of thistype here involved is materially ing throughout the length of thearticle. minimized and at the same time the advantages as- Itis-characteristic of high frequency furnaces of such'a coil areretained. This is accomplished 28 employing such a coil within asusceptor howby providing at the ends of the cylindrical type ever, thatthe susceptor does not heat uniformly of coil inwardly converged orconverging coil exthroughout its cross section due to the fact thattensions which serve to direct the magnetic flux the magnetic field doesnot penetrate sufficiently more obliquely to or more toward thesurroundso into the susceptor away or outwardly from the ing article,thereby providing a better distribu- 80' coil. When electromagneticenergy flows into tion of the magnetic flux and greater induc-' theinterior of a conducting means, its convertance while still maintainingthe same good cousion into heat starts at the surface whereit enpiingwithin the central section of the coil. The ters and diminishes at everypoint distant beconverged or converging end construction causes yond thesurface. Also this peripheral heating a more rapid heating of the endportions of an 86- is not distributed uniformly along its length dueobject located externally around the central secto the fact that thestrongest field is midway tion of the coil and increases the control ofheat between the ends of the coil with the result distribution anduniformity of heating, as desired, that the conversion of energydiminishes markalong the length of the article to be heated,

o edly along the axial direction of the coil as the due to the increasein strength of the magnetic 0 distance from the centeroutwardly towardthe field induced therein which results in a more ends increases. Forexample, in a wheel hub efficient heating apparatus. The distributionhaving a cylindrical inside surface surrounding of the magnetic fluxaround this novel coil is a cylindrical coil of about the same length,the considerably better than a coil without extengreater part of theelectromagnetic energy sions since the shape of the coil follows more 5around the coil that is converted into heat in closely the path of themagnetic flux and rethe inner cylindrical "skin of the object isduces'flux interthreadlng through the coil. low in efllciency anddistributed very unevenly With the foregoing observations in mind, thealong its length, and the fact that the ends of principal object of thepresent invention is to the objectreside in a much less intense heatingprovide an induction coil which is constructed so region of the coil isevidenced by the visible and arranged to direct magnetic flux moreobreddening of the cylindrical surface near the liquely to or moretoward a susceptor located center when an object of considerable lengthis externally about the coil, and this and other obfirst heated, whilethe end portions of the object Jects of the invention, as well as thefeatures remain black for a considerable period becoming and details ofits" construction and operation. 55 I are hereinafter fully set forthand shown in the accompanying drawing, in which:

Figure l is a vertical section through an induction coil made accordingto this invention;

Figures 2 and 3 are diagrammatic illustrations showing modifiedarrangements of an induction coil embodying said invention;

Figure 4 is a diagrammatic view of a high frequency inductive heater orfurnace embodying a coil made according to the present invention; and

Figure 5 is a vertical section of still another form of coil embodyingsaid invention.

As pointed out above, the invention consists essentially in theconstruction of an induction coil to provide at its ends portionsarranged in inwardly converging or oil'set relation in contrast to theconventional cylindrical type of coil. The flux or magnetic field thusset up externally of the coil is directed more obliquely to or moretoward a susceptor placed thereabout, and referring to the drawing, aninduction coil made according to the present invention may be composedof a continuous single layer or winding of relatively fiat or roundtubular wire i wound to form a lower diverging portion A whichterminates at its upper end in a central portion B of cylindrical shape,which in turn, terminates at its upper end in an inwardly convergingportion C. In some cases it may be desired to have the central portion Bof the coil conform to the cross-sectional shape of an irregular objectplaced thereabout to be heated and, therefore, it is understood that theinvention embraces such modification.

The induction coil is preferably wound upon a suitable mandrel having asurface configuration which conforms approximately to the desiredcontour of the coil. The angles at which the opposite end sections A orC are disposed with respect to the central section B may be varied asdesired to suit performance requirements, and the number of turns perunit of length in the same or other sections of the coil need not beuniform therein. Furthermore, the number of turns or coils of wireemployed in the end portions A or C of the coil may vary as desired toprovide any desired ratio between the number of turns or coils of wirein the said portions A or C and the central portion B and, of course, asthe length of the said central portion B decreases or is decreased, themore critical or narrow will become the region of concentration of themagnetic field thereabout. The limiting case of this involves a coilsuch as that shown in Figure 5 of the drawing wherein the centralsection B' is of minimum length or height having but a single turn. Anarrangement such as this enables concentrated heating of a small lengthof a susceptor and at the same time, the advantages of a multiple turncoil are retained.

The induction coil contemplated by this invention is not restricted tothe particular configuration or shape illustrated in Figure 1 of thedrawing, and similar results are obtained, for example. by constructingan induction coil to provide at opposite ends of the central portion Bportions A or C' which curve concavely inwardly and axially of the, coilas shown in Figure 2 or as shown in Figure 3 wherein inwardly andaxially curving convex portions A" or Cf, respectively, are provided atopposite ends of a central portion B". Other forms and shapes may,however, be employed with satisfactory results.

By directing the fiux or magnetic field more toward the susceptor orarticle to be heated, a coil constructed in accordance with this inven-5 tion may be employed to advantage to materialb' increase theefficiency of heat treating apparatus such as high frequency furnaces,one form of which is shown in Figure 4 of the drawing, and comprises aninduction coil 3 suitably mounted within a susceptor 4 and spacedtherefrom by suitable insulation indicated by reference numeral 5,although in some cases no insulation is needed or desirablef As shown,the induction coil I comprises a plurality of turns of wire wound to thegeneral shape or form shown in Figure l and consists of a centralportion B and inwardly converging end portions A and C, a high frequencycurrent being supplied to said coil 3 through the extrem- -ities of theend portions 8 and 1 thereof or at intermediate points as desired. Forthe purpose of cooling the coil, water or other cooling fluid may bepassed through the tubular wire forming said coil through the openingsaflorded at the extremities of the end portions 8 and I or atintermediate points of the coil. Use of the coil 3 for heating purposesas described is confined essentially to the central portion thereof inorder to obtain maximum coupling and consequently maximum heating of thesusceptor, and so that the inwardly and axially converging end portionsA and C thereof will function fully to direct the magnetic field moreobliquely to and more toward the susceptor to be heated so that theentire length of the object may receive the full force or action of suchfiux or magnetic field. The heating efilciency and control of heatdistribution of the coil is thus materially increased with the resultthat the length of time required to heat an object, the amount of powerconsumed, and equipment necessary are each substantially reduced. Insome instances of use of the coil where it is desired to further aid incompletion of the magnetic path through the coil, it may be desirable toplace steel laminae within said coil.

While my description of the invention has been confined to theembodiment or adaptation thereof to high frequency induction heaters andfurnaces, it will be obvious, of course that the use of said inventionis not limited to a device of that nature butmay be employed toadvantage in any instance where it is desired to obtain a maximummagnetic field strength in a susceptor about the coil and where thelength of the central portion is decreased the more narrow or criticalis the region of concentration of the magnetic field thereabout.

I claim:

1. An inductive heating device comprising an induction coil consistingof a winding of wire having a central heating portion of wire arrangedfor disposition within a susceptor to be heated,

and end portions of wire arranged in inwardly flafi'set relation withrespect to said central nor.-

2. An inductive heating device comprising an induction coil consistingof a winding of wire having a central substantially cylindricalportion 1. arranged for disposition within an object to be heated, andend portions leading fromthe ends of said central cylindrical portionand offset with respect thereto in a direction toward the axis of thecoil, said end portions constituting means for 1.

' amaeao directing the lines of flux more toward the object to beheated.

3. An inductive heating device comprising an induction coil consistingof a winding oi wire having a substantially straight-sided heatingportion arranged for disposition within a susceptor to be heated, andend portions oflset inwardly toward the axis with respect to thestraight-sided portion to control the distribution of heat in thesusceptor alongthe axial direction thereof.

4. An inductive heating device comprising an induction coil consistingof a winding otwire having a central substantially cylindrical portionconsisting of at least one turn of the wire arranged for dispositionwithin a susceptor to be heated, and end portions ofl'set inwardly withrespect to the central portion, said end portions constituting means fordirecting the magnetic flux more toward the susceptor.

5. An inductive heating device comprising an induction coil consistingof a winding of wire having a central substantially straight-sidedportion arranged for disposition within a susceptor to be heated andcurving end portions leading away from the ends of said central portionand onset with respect thereto in a direction toward the axis of thecoil.

6. An inductive heating device comprising an induction coil consistingof a winding of wire having a central heating portion conformingsubstantially to the internal contour of and arranged for dispositionwithin a susceptor to be heated and end portions arranged in inwardlyoffset relation with respect to the central portion, said end portionsconstituting means for controlling the disnae disposed within the coilfor the purpose'of improving and controlling the magnetic path in thecoil. i

' D AVID 'PISAREV.

